Acetylene-terminated polyimide oligomers show promise as matrix resins for advanced aircraft and aerospace systems. The materials have the potential of curing without the evolution of volatile by-products, thereby obviating the problem of voids formation in composite structures and molded articles. Unfortunately, the acetylene-terminated oligomers generally display a very narrow processing window as a result of a comparatively rapid gel formation at cure temperatures. For example, gel times of 1 to 3 minutes at cure temperature of about 485.degree. F. are not unusual. Because of the short flow period before gelation occurs, it becomes necessary to control processing parameters very closely, thereby causing difficulties in the fabrication of fiber reinforced composites, adhesives in bonded joints and in injection or compression molded components or parts. In Application Ser. No. 967,049, filed on Dec. 6, 1979, now U.S. Pat. No. 4,187,359 issued Feb. 5, 1980, it is disclosed by one of us as a coinventor that trinitroloacetonitrile is an effective additive for retarding the rate of cure of acetylene-terminated polyimide oligomers. It would be desirable to provide other compounds that would have a similar effect when added to the oligomers.
It is an object of this invention, therefore, to provide additives for acetylene-terminated polyimide oligomers that retard their rate of cure.
Another object of the invention is to provide acetylene-terminated polyimide oligomer compositions having a retarded cure rate as compared to the oligomer per se.
Another object of the invention is to provide a method for retarding the rate of cure of acetylene-terminated polyimide oligomers.
Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure.